1. Field of the Invention
The present invention relates to a reflector-mirror drive shaft controller which makes it possible to use unskilled operators in operating a laser beam machine, maximize quality and productivity for each material and workpiece thickness, and accomplish long, unattended operation under optimum machining conditions.
2. Description of the Related Art
Conventionally, laser machining involves placing a lens at an end of an optical path of a laser beam emitted from a laser oscillator device, setting a workpiece near the focal position of the lens, and machining the workpiece through instantaneous evaporation.
The focal length of the machining lens greatly affects machining and the optimum focal length varies with the material and workpiece thickness. Thus, it is necessary to keep machining lenses with different focal lengths on hand, select the optimum focal length in each case according to the material and workpiece thickness, and make proper settings manually. The machining lens with the optimum focal length for the material and workpiece thickness is selected.
However, when the material and workpiece thickness change continuously, it is practically impossible to prepare machining lenses of focal lengths which vary continuously and steplessly, making it necessary to prepare several machining lenses of typical focal lengths which vary stepwise (e.g., 2.5 inches, 3.5 inches, 5.0 inches, 7.5 inches, etc.) based on experience.
There is a known technique which maintains optimal distance between a condenser lens and workpiece using beam diameter measured by a laser beam diameter detector installed below the condenser lens (see Japanese Patent Laid-Open Publication No. 7-51875 (Patent Document 1)).
When a machining lens with a certain focal length is selected, the lens is designed to machine workpieces in a certain thickness range (e.g., workpiece thickness: a to b mm).
In that case, machining quality produced by the machining lens with the selected focal length has a normal distribution between a and b.
Maximum machining quality is available only for one workpiece thickness between a and b. Other thicknesses do not provide the maximum machining quality, but they provide practically acceptable quality based on personal judgment of the operator.
In other words, the maximum quality is not available except for one workpiece thickness.
Similarly, there also exists a maximum machining speed between a and b, meaning that the maximum machining speed is not available for every workpiece thickness. Thus, maximum productivity is not available.